300 PRACTICAL ORGANIC CHEMISTRY
' It is also much more easily oxidised than toluene to benzole
< i Q5IIr,CILCl -i- Oo = CaIInCOOII + HC1.
Benzal chloride and -benzotrichloride are also decomposed by
i • water, the former in presence of calcium carbonate, and the
i latter at a high temperature^ yielding, in the one case, benxalde-
" hyde, and in the other, benzoic acid,
CJIflCHCla + II.20 = C,jIIsCOII + 2IIC1.
C(JU5CC1, + 2lI2O = C,5HaCO.OII + 3IIC1.
J Benzoic acid.
^ PREPARATION 87.
Benzyl alcohol may be also obtained by the action of caustic
potash on benzaldehyde (see Reaction 4, p. 197). This reaction
JH'*j} is specially characteristic of cyclic-compounds containing an
! 11 aldehyde-group in the nucleus, although some of the higher
aliphatic aldehydes behave in a similar fashion (Cannizzaro),
2CCH5COH -I- KOH = C0H5CH,Oir + QIIsCOOK.
Benzyl alcohol. Potassium benzoate.
Benzyl alcohol has the properties of an aliphatic alcohol, and
not those of a phenol. On oxidation, it gives benzaldehycle
and benzoic acid, and it forms benzyl esters with acids or acid
Benzaldehyde.—The aldehydes of the aromatic series
may also be obtained by the oxidation of a methyl side-chain
with chromium oxychloride. The solid brown product,
C(.H5CH3(CrO2Cl2)2, formed by adding CrO2Cl2 to toluene,
dissolved in carbon bisulphide, is decomposed with water, and
benzaldehyde separates' out (Etard). Other methods for pre-
paring aromatic aldehydes are (i) the Friedel-Crafts reaction, in
which a mixture of carbon monoxide and hydrogen chloride are
passed into the hydrocarbon in presence of aluminium chloride
and a little cuprous chloride,
C6H,.CH8 + HC1.CO = Ct!M/ ' + HC1 ;